Limits

Candice has the ability to disguise herself as another person with a nearly flawless illusion. Her ability can apparently fool all five senses: sight, sound, smell, touch, and taste. When she was impersonating Sandra Bennet, Mr. Bennet literally held her and kissed her without penetrating the disguise (Parasite).

Candice does not necessarily have to have met an individual she is impersonating. She was able to impersonate Simone Deveaux, although they apparently never met before Simone's death, and Candice had not seen Simone's dead body until after she appeared in her form. How she was able to accomplish this feat is unknown.

Candice can also create illusions in her vicinity. She was able to hide Simone Deveaux's body from police, and she kept Micah Sanders from escaping the Company's Kirby Plaza facility by making it seem that every path he took lead back to her. She can make people think she is two people at the same time. She claims that she can make a person see anything she wants them to see.

Future Sylar extensively used this power to disguise himself as President Nathan Petrelli. His use of this power in a possible future demonstrates that illusions can fool electronic equipment like cameras, since he was able to disguise himself on national television.

Crazy Tom has shown he is capable of casting illusions over anything he touches. He uses his ability to cast an illusion of himself instantaneously melting chains that are touching him into a pair of jeans and a T-shirt. (The Agent) He has also shown he is capable of changing his outfit into a straitjacket and tux. (The Agent)

He is also capable of at least temporarily changing other people's clothes. (The Agent)

Callum demonstrated this ability by creating an illusion of the man for whom Trevor Tanaka was looking, an illusion of the hallways and attic of a house, and an illusion of himself that interacted with others. (Faction Zero)

Notes

In the episode commentary for Parasite, Allan Arkush and Christopher Zatta discuss Candice's power. Zatta says he believed it was important that Candice's ability be a mental one -- that is, to appear like other characters rather than to physically become other characters -- to be more in keeping with the other powers in the show.

As of .07%, the special effect used to show Candice's power has changed. Previously, it was shown as a "shimmery" effect that impacted much of the area around her. Now, it is shown as a "morph" effect that affects only her.

Micah theorizes that Candice's ability stems from bending light (Landslide). While this would explain how the ability fools cameras, it does not explain how she maintains her disguises when physically interacting with other characters.

Regarding the redhead student's facial afflictions caused by Betty, Ryan Odagawa said in an email, "It is supposed to be boils, and her face is 'both rotting and peeling off her head'...It was supposed to be hanging off her face and rotting."

When knocked unconscious (How to Stop an Exploding Man), Candice reverts from her Jessica disguise to her usual young, female appearance; her illusion of Micah lying dead on the floor also disappears. It is not clear why she reverts to her "standard" disguise when knocked out instead of reverting to her true appearance (Betty, Part 2).

Illusion appears to be an aspect of telepathy. Using his ability, Maury Parkman created an illusion of D.L. that was visible to Niki, but not to Mohinder, who was also present at the time (Out of Time). On another occasion, Maury created an illusion that trapped both his son and Nathan in a dream-like state. Additionally, Matt used his power to create an illusion to escape Knox (Eris Quod Sum). It is unknown if the illusions created in this fashion can be extended to anyone viewing the scene or are specific to those being telepathically targeted.